The invention relates to a saddle-shaped coil winding using superconductors on a tube outer surface with axially running straight winding sections and winding sections bent between them on opposite end faces, forming end windings. The invention also relates to a method for production of a coil winding such as this. A corresponding method for production of a coil winding such as this is disclosed in JP 06-196314 A.
In the field of superconduction technology, saddle-shaped coil windings have been provided for a long time in the field of high-power and particle physics, or electrical machines. In this case, the conductors that are used are generally composed of a traditional, metallic superconductor material with a low critical temperature Tc, so-called low-Tc superconductor material (abbreviation: LTS material). This is because appropriate conductors can be bent relatively easily, and without any reduction in their superconducting characteristics, to the saddle shape with axially running, straight winding sections and with winding sections which are bent between them on opposite end faces and form end windings. Alternatively, their superconducting characteristics are formed or set, using the so-called “Wind and React” technique, only after final shaping of the conductors in the winding.
As is known, attempts have been made using oxidic superconductor materials with a high critical temperature Tc, the so-called high-Tc superconductor material (abbreviation: HTS material) to produce corresponding windings with conductors composed of these materials, as well. JP 06-196314 A, which was cited initially, contains a proposal for this purpose. JP 2003-255032 A also mentions the option of using a conductor such as this for saddle-shaped coil windings. However, this results in the problem that, until now, it has been possible to produce conductors using materials such as these with an adequate current carrying capacity or critical current density Jc only in strip form, although completed strip conductors are highly sensitive to strain, and therefore can be bent only to a very minor extent without the risk of reductions in their current carrying capacity or critical current density Ic. To a major extent, saddle-shaped coil windings have therefore not been produced using HTS conductors in the form of strips such as these, and so-called “racetrack coils” have been planned instead of this.
Racetrack coils are flat windings in which the turns always lie within a winding plane. If racetrack coils such as these are stacked one on top of the other, the stack therefore has no opening (so-called “aperture”) in the longitudinal direction. In rotating machines with a shaft running all the way through them, racetrack coils must therefore be fitted above and below a central area (see for example DE 199 43 783 A1). This therefore results in a free space, which is not occupied by the winding and leads to a corresponding reduction in the useful field strength, in the axially running straight winding sections of the coil winding. An aperture is created by the use of saddle coils, that is to say coil windings with end windings bent up at the ends. This is associated with more effective use of the superconducting windings, for example in rotating machines, provided that the superconductors can be deformed appropriately without any adverse effects on their superconducting characteristics.
Flat coil windings of the racetrack type for an HTS motor and the production of corresponding coil windings are also described, for example, in “IEEE Trans. Appl. Supercond.”, Vol. 9, No. 2, June 1999, pages 1197 to 1200.
Conically shaped coil windings with HTS conductors in the form of strips have also been proposed (see WO 01/08173 A1). In the case of this coil geometry, the winding is admittedly curved; however, in this case as well, the conductors of the individual turns on the straight sections and in the end winding areas are each located within a common plane. The flat faces of the conductors in this case lie parallel to the axis, which emerges at right angles from the coil winding.
Attempts are also known to produce saddle-shaped coil windings using HTS conductors in the form of strips (see “IEEE Trans. Appl. Supercond.”, Vol. 9, No. 2, June 1999, pages 293 to 296). The winding design described there allows only small apertures for a quadrupole magnet, however; however, apertures such as these are not sufficient for dipole windings, such as those which must be provided for two-pole rotor windings in machines.
A production method which is known for coil windings composed of strain-sensitive superconductors is based on the idea that the superconducting characteristics of the conductors of the coil winding are formed only after the winding process, in their final shape (so-called “Wind and React” technique; see for example EP 1 471 363 A1). However, this generally requires complex winding apparatuses, which are not very suitable for cost-effective production of coil windings for replacement in rotating machines.